Yup, I discovered this myself. There was a pretty long discussion about it on the Technical forum recently.
I'm currently powering the Empeg off of a few different wall-wart power supplies that were meant for other equipment. At the moment, it's playing quite nicely off of a 15v power supply that was meant for a flatbed scanner. In fact, I hardly ever use the scanner, so I'm leaving it unplugged most of the time and powering the Empeg with that supply almost exclusively.
I've also been able to drive it using the 15v power supplies that Altec Lansing makes for their little multimedia speakers. The beauty of this (as I've mentioned elsewhere) is that you don't have to carry the power supply with the Empeg when you want to move it from room to room (or home to office, or whatever).
One word of caution: Test the power supply voltage before you actually plug it in. Just because it says "15v" doesn't mean that's what it puts out. The speaker power supplies I'm using are actually putting out 18v (which Hugo said was OK).
Also, the amperage of the power supply is a consideration. I tried a 15v 450ma supply that was insufficient for the Empeg (it kept rebooting when the display fired up). The 15v 800ma power supplies I tried seem to be OK.
-- Tony Fabris -- Empeg #144 --
Caution: Do not look into laser with remaining good eye.